High Rev's possible with high displacement?
nubtuner
11-10-2004, 01:41 AM
Before anybody flames me I looked through the forums, but I did not see anything particularly useful to my question, which is.....
What generally prohibits High displacement engines from making high revs? I say generally because I know it won't be just one engine part, but a combination of things. I've heard of things like weight of parts? Position of the block? etc..., but those don't sound like anything that can't be done to bigger displacement engines. Can't big blocks use the same technology as smaller one?
Also, how do F1 engines get such high revs? And why do they keep such low displacement?
The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.
I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.
PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.
What generally prohibits High displacement engines from making high revs? I say generally because I know it won't be just one engine part, but a combination of things. I've heard of things like weight of parts? Position of the block? etc..., but those don't sound like anything that can't be done to bigger displacement engines. Can't big blocks use the same technology as smaller one?
Also, how do F1 engines get such high revs? And why do they keep such low displacement?
The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.
I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.
PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.
curtis73
11-10-2004, 04:16 AM
Before anybody flames me I looked through the forums, but I did not see anything particularly useful to my question, which is.....What generally prohibits High displacement engines from making high revs? I say generally because I know it won't be just one engine part, but a combination of things. I've heard of things like weight of parts? Position of the block? etc..., but those don't sound like anything that can't be done to bigger displacement engines. Can't big blocks use the same technology as smaller one?
In general, it is weight that is the big issue. I won't post numbers, but inertia and acceleration are exponential figures. Adding a few ounces to a piston at 5000 rpms is like adding several tons of inertial weight. Certain engines are more suited to high RPMs than others; for instance: The Buick 455 has a 4.313" bore and 3.9" stroke. Contrast that with the Olds 455 at 4.126" and 4.25". The shorter stroke lends itself to higher RPMs three ways; 1) bigger bores allow for larger unshrouded valves which in general promotes better breathing, 2) the inertia created from a 3.9" stroke is much less than that of a 4.25" stroke., 3) The bore/stroke ratio and corresponding rod/stroke ratio that can be acheived allows longer piston dwell. This allows for more of the combustion pressure to act on the piston at its best points in the stroke.
Also, how do F1 engines get such high revs? And why do they keep such low displacement?
Those two go hand in hand. HP is achieved with RPMs. They have the luxury of using small, light engines spinning very fast to make power. They are also geared so that they can stay in that RPM band all the time. F1 engines make such high revs (this will sound sarcastic but its just the truth) because they have $6million to spend on R&D and $100,000 to spend on each engine. They use some pretty exotic metals, designs, and techniques to make an engine that will rev to 15,000 rpms. You also have to keep in mind that they rev that fast for 500 miles and then they are rebuilt or scrapped. A Buick 455 would probably rev to 8000 with the proper breathing and cam, but it might only last 500 miles as well.
The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.
You are right. In today's world, its easier to take a small engine that is easy on emissions and fuel usage, and make it spin to 7000 so that you can advertise big HP numbers to the public. Take a look at the Honda S2000. Some people like them as daily street vehicles, but I"m not a big fan of them. I got tired of the constant struggle to get enough RPMs to make power. The automakers have fleeced the general public into thinking that HP is the number they want, when its actually torque that is the "drivability" part of the equation.
I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.
I like how you think, but there is a problem with the theory. Taking your example; the Viper engine makes 525 tq at 4200. If you spun it (in its current configuration) to 7200 rpms, you would have almost zero net torque. You almost certainly wouldn't even have enough to spin the engine anymore. If you notice the current torque curve on the viper 8.3 starts falling and is slim to nill at 7200. Your math is however correct. If you could get a viper to make 525 tq at 6000, you would have a real hp monster. The problem is to get that, you would need extreme intake port flow on the heads, a massive cam, and you would lose the 525 you used to have at 4200. You have then made monster HP, but you'd have to gear it so that achieving that HP can happen. You've basically killed low RPM torque, so you have to lower the rear end ratio to multiply the torque you have remaining. Then, once you get up to the RPM where power is being made, you're in for one heckuva ride. Basically, you've taken a streetable engine and made it a race-only engine.
PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.
A subscription to Hot Rod, Car Craft, or similar mags will help immensely, but only after conscious reading for several months. I suggest listening to others who reply here, since I can't get my point across without five long paragraphs. :)
Basically, high RPM engines need tons of flow. Low RPM engines need velocity. Adding flow typically slows velocity. If no one else replies with a concise answer, I'll give you my long answer but lets see first :).....
In general, it is weight that is the big issue. I won't post numbers, but inertia and acceleration are exponential figures. Adding a few ounces to a piston at 5000 rpms is like adding several tons of inertial weight. Certain engines are more suited to high RPMs than others; for instance: The Buick 455 has a 4.313" bore and 3.9" stroke. Contrast that with the Olds 455 at 4.126" and 4.25". The shorter stroke lends itself to higher RPMs three ways; 1) bigger bores allow for larger unshrouded valves which in general promotes better breathing, 2) the inertia created from a 3.9" stroke is much less than that of a 4.25" stroke., 3) The bore/stroke ratio and corresponding rod/stroke ratio that can be acheived allows longer piston dwell. This allows for more of the combustion pressure to act on the piston at its best points in the stroke.
Also, how do F1 engines get such high revs? And why do they keep such low displacement?
Those two go hand in hand. HP is achieved with RPMs. They have the luxury of using small, light engines spinning very fast to make power. They are also geared so that they can stay in that RPM band all the time. F1 engines make such high revs (this will sound sarcastic but its just the truth) because they have $6million to spend on R&D and $100,000 to spend on each engine. They use some pretty exotic metals, designs, and techniques to make an engine that will rev to 15,000 rpms. You also have to keep in mind that they rev that fast for 500 miles and then they are rebuilt or scrapped. A Buick 455 would probably rev to 8000 with the proper breathing and cam, but it might only last 500 miles as well.
The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.
You are right. In today's world, its easier to take a small engine that is easy on emissions and fuel usage, and make it spin to 7000 so that you can advertise big HP numbers to the public. Take a look at the Honda S2000. Some people like them as daily street vehicles, but I"m not a big fan of them. I got tired of the constant struggle to get enough RPMs to make power. The automakers have fleeced the general public into thinking that HP is the number they want, when its actually torque that is the "drivability" part of the equation.
I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.
I like how you think, but there is a problem with the theory. Taking your example; the Viper engine makes 525 tq at 4200. If you spun it (in its current configuration) to 7200 rpms, you would have almost zero net torque. You almost certainly wouldn't even have enough to spin the engine anymore. If you notice the current torque curve on the viper 8.3 starts falling and is slim to nill at 7200. Your math is however correct. If you could get a viper to make 525 tq at 6000, you would have a real hp monster. The problem is to get that, you would need extreme intake port flow on the heads, a massive cam, and you would lose the 525 you used to have at 4200. You have then made monster HP, but you'd have to gear it so that achieving that HP can happen. You've basically killed low RPM torque, so you have to lower the rear end ratio to multiply the torque you have remaining. Then, once you get up to the RPM where power is being made, you're in for one heckuva ride. Basically, you've taken a streetable engine and made it a race-only engine.
PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.
A subscription to Hot Rod, Car Craft, or similar mags will help immensely, but only after conscious reading for several months. I suggest listening to others who reply here, since I can't get my point across without five long paragraphs. :)
Basically, high RPM engines need tons of flow. Low RPM engines need velocity. Adding flow typically slows velocity. If no one else replies with a concise answer, I'll give you my long answer but lets see first :).....
benchtest
11-10-2004, 05:37 AM
Curtis hit most of the reasons quite well. Weight is #1. You're throwing a lot of mass around in there. You can build a light-weight set-up and rev it higher, but longevitiy is lost. A 1/4 mile engine can turn 9000, but it only has to do it for 9 seconds or less. Also consider that burn-time is fairly fixed. As you rev higher, you have less and less time for the flame to travel across the cylinder. Big engines have big bores, and long flame travel. We're talking milliseconds here. It boils down to the horsepower formula...torque and horsepower are going to cross at 5252. Horsepower will win after that. Does that help you at all?
Alastor187
11-10-2004, 07:29 AM
Also, how do F1 engines get such high revs? And why do they keep such low displacement?
The primary driving force of engine configuration in any F1 car is the rules and regulations. Currently F1 engines are limited to 3.0 liters but next year this will drop to 2.4 liters. Also, they are prevented from using forced induction. So their solution to get large amounts of power from a small displacement naturally aspirated engine was "higher rpms".
As was already stated that there are any number of issues with extremely high revving engines. I would also like to add that friction will increase non-linearly with engine speed, not only reducing the net power output but also increasing internal temperatures.
Also, the issue with flow rate and flow velocity stem from the inertia of the air/fuel mixture. Because the mixture has inertia at higher rpms the mechanical response of the valves actually becomes better than the fluid response of the mixture. So a different cam profile is needed to overcome the high rpm fluid response time. Negatively, a high rpm cam tends to reduce low rpm performance and vice-versa.
The primary driving force of engine configuration in any F1 car is the rules and regulations. Currently F1 engines are limited to 3.0 liters but next year this will drop to 2.4 liters. Also, they are prevented from using forced induction. So their solution to get large amounts of power from a small displacement naturally aspirated engine was "higher rpms".
As was already stated that there are any number of issues with extremely high revving engines. I would also like to add that friction will increase non-linearly with engine speed, not only reducing the net power output but also increasing internal temperatures.
Also, the issue with flow rate and flow velocity stem from the inertia of the air/fuel mixture. Because the mixture has inertia at higher rpms the mechanical response of the valves actually becomes better than the fluid response of the mixture. So a different cam profile is needed to overcome the high rpm fluid response time. Negatively, a high rpm cam tends to reduce low rpm performance and vice-versa.
RandomTask
11-10-2004, 09:13 AM
Guys! You forgot to flame him! ;) Excellent question nubtuner :) . I just have to post some basic things here before curtis's intelligence makes me crawl under my desk and start sucking my thumb...
Vipers redline at 5500/6K RPM.
Formula cars rev up to 20K RPM.
Alastor, are you sure they're going to 2.4liters next year? I heard BMW just finished designing their motor for next season and its a 3.0Liter? I could be wrong :(.
Just to emphasize this on curtis's explanation: A Suzuki GSXR 600CC (0.6Liters) comes stock with 105 HP but only 45ft/lbs of torque. However the motor gets this HP at 13,500+RPM.
Vipers redline at 5500/6K RPM.
Formula cars rev up to 20K RPM.
Alastor, are you sure they're going to 2.4liters next year? I heard BMW just finished designing their motor for next season and its a 3.0Liter? I could be wrong :(.
Just to emphasize this on curtis's explanation: A Suzuki GSXR 600CC (0.6Liters) comes stock with 105 HP but only 45ft/lbs of torque. However the motor gets this HP at 13,500+RPM.
clawhammer
11-10-2004, 12:30 PM
^Don't be so hard on him. He's just trying to learn. There are no stupid questions. It's among the easiest ways of learning.
Kven
11-10-2004, 12:46 PM
formula 1 cars can rev high also due to their bore size; most of them are v10's; so each cylinder displaces about 300cc...Honda's B16 displaces 400cc per cylinder.
RandomTask
11-10-2004, 02:01 PM
claw, sarcasm? I thought it to be an excellent question, if you read the post :).
Kven, are you trying to compare a Honda B16 block to Formula Racing?--Lets do math here:
1000HP/10 cylinders=100hp per cylinder
where as
140HP/4 Cylinder= 35 hp per cylinder
Better yet;
1000hp/3000cc=0.333hp/cc
140hp/1600cc=0.0875hp/cc
I still don't understand the relavance of your comparison ;)
Kven, are you trying to compare a Honda B16 block to Formula Racing?--Lets do math here:
1000HP/10 cylinders=100hp per cylinder
where as
140HP/4 Cylinder= 35 hp per cylinder
Better yet;
1000hp/3000cc=0.333hp/cc
140hp/1600cc=0.0875hp/cc
I still don't understand the relavance of your comparison ;)
drdisque
11-10-2004, 02:41 PM
F1 engines also have no camshafts, the valves are opened and closed electronically.
Kven
11-10-2004, 03:35 PM
no im not comparing power; im comparing that small cylinders rev faster; like the puny glow engines used in rc cars, they rev up to like 21,000rpm super easy and pretty quick.
Alastor187
11-10-2004, 03:51 PM
Alastor, are you sure they're going to 2.4liters next year? I heard BMW just finished designing their motor for next season and its a 3.0Liter? I could be wrong :(
You are right, the 2.4L V-8 restriction wont be active until January 1st, 2006. As well, there will be an exception through 2006 and 2007 for 3.0L V-10 with limited peak rpms.
You are right, the 2.4L V-8 restriction wont be active until January 1st, 2006. As well, there will be an exception through 2006 and 2007 for 3.0L V-10 with limited peak rpms.
curtis73
11-10-2004, 04:32 PM
There are no stupid questions. It's among the easiest ways of learning.
Before you say that, read this one I got caught in...
http://www.automotiveforums.com/vbulletin/showthread.php?t=314378
The guy wants to check his float level and keeps begging for his info or he'll be "in deep sh--". I asked him make, model, year, and engine, and he told me its either a Toyota, Ford, Mitsubishi, or Mazda but he can't tell. Its an engaging read. I know he just wants his info, but he won't tell me what I need to know.
I'm sure he's a fine gentleman, but...
Before you say that, read this one I got caught in...
http://www.automotiveforums.com/vbulletin/showthread.php?t=314378
The guy wants to check his float level and keeps begging for his info or he'll be "in deep sh--". I asked him make, model, year, and engine, and he told me its either a Toyota, Ford, Mitsubishi, or Mazda but he can't tell. Its an engaging read. I know he just wants his info, but he won't tell me what I need to know.
I'm sure he's a fine gentleman, but...
Reed
11-10-2004, 07:28 PM
i may be wrong but i thought that one of the main reasons that formula one engines have such high revs because of their extremely short strokes but are able to produce such high hp because of the large bore and high revs. if i am wrong please correct me and fell free to add anything if i am right because i have been trying to find info and specs on f1 engines.
CBFryman
11-10-2004, 07:42 PM
also, F1 engines make 0-nil torque at say 3,000-4,000RPM... its like rotaries. i love 'em but in daily driving when passing (i dont onwn one but i have driven a few FC's and FD's) you have to bring revs up to 4,000 to make good power on the NA 13B's. roataries are able to make such high RPM's because the piston never has to stop and change directions. it just goes around and around and around in a eliptical motion.... stock redline of like 9,500. able to make a streetable 13,000RPM monster...
Kven
11-10-2004, 08:10 PM
f1 cars make their hp mainly through revs; they make only about 250-300lbs of torque. the large bore is so they can have the displacement they want but retain the small stroke.
nubtuner
11-10-2004, 11:55 PM
Thanks to everyone for helping me out. I've also done some more research into this topic, and I've learned a lot. I would like to recap everything with you guys though. Make sure i got everything right .
Here's what I've got, to increase RPM's of an engine one would generally have to decrease the inertia forced on the parts (i.e. weight reduction, shorter stroke) and increase the flow. Am I on the right track?
If so I have some more ?'s for you guys:biggrin:.
1) What are ways that I can increase flow? A better exhaust would help out I know, but what about the valvetrain? What are the technical benefits of a SOHC (i.e. I4's) vs DOHC (i.e. V6's) vs the electronic Hydraulic systems of F1 cars vs any experimental things like the Coates CRVS (I know they have problems with sealing, but I'm talking about the theory behind it)? I know that the F1 systems are the best right now, but why (in technical terms)? And also why aren't there any companies making aftermarket headers using that technology?
2) I understand how Bore/stroke come into play, but are there any formulas for the trade off between them? Ex. if I wanted to keep the same displacement(power) but shorten the stroke, how would I figure out how much to increase the bore? Would it be a 1-to-1 ratio or something like that? Also I know the more you bore out an engine the weaker the walls of the chamber are, but are there any restrictions on shortening the stroke? And is there anyway to reinforce the combustion chambers walls to handle a higher bore?
3) I don't understand why I wouldn't be able to keep the low end power when I increase the RPM's of a low end engine like in my viper ex. It might be because I don't quite understand how an engines powerband is constructed. If someone could explain this in detail that would be AWESOME!!! Even just pointing me to a site with good charts would help me out a lot.
ok, I think that's enough questions to keep you guys busy for a week at least:lol:.
Again, thanks to everyone that posted!!! You guys rock.
Here's what I've got, to increase RPM's of an engine one would generally have to decrease the inertia forced on the parts (i.e. weight reduction, shorter stroke) and increase the flow. Am I on the right track?
If so I have some more ?'s for you guys:biggrin:.
1) What are ways that I can increase flow? A better exhaust would help out I know, but what about the valvetrain? What are the technical benefits of a SOHC (i.e. I4's) vs DOHC (i.e. V6's) vs the electronic Hydraulic systems of F1 cars vs any experimental things like the Coates CRVS (I know they have problems with sealing, but I'm talking about the theory behind it)? I know that the F1 systems are the best right now, but why (in technical terms)? And also why aren't there any companies making aftermarket headers using that technology?
2) I understand how Bore/stroke come into play, but are there any formulas for the trade off between them? Ex. if I wanted to keep the same displacement(power) but shorten the stroke, how would I figure out how much to increase the bore? Would it be a 1-to-1 ratio or something like that? Also I know the more you bore out an engine the weaker the walls of the chamber are, but are there any restrictions on shortening the stroke? And is there anyway to reinforce the combustion chambers walls to handle a higher bore?
3) I don't understand why I wouldn't be able to keep the low end power when I increase the RPM's of a low end engine like in my viper ex. It might be because I don't quite understand how an engines powerband is constructed. If someone could explain this in detail that would be AWESOME!!! Even just pointing me to a site with good charts would help me out a lot.
ok, I think that's enough questions to keep you guys busy for a week at least:lol:.
Again, thanks to everyone that posted!!! You guys rock.
sierrap615
11-11-2004, 12:28 AM
while we are on the subject heres a link i think you guys will like. it runs at 102 RPM
http://www.bath.ac.uk/~ccsshb/12cyl/
http://www.bath.ac.uk/~ccsshb/12cyl/
nubtuner
11-11-2004, 01:53 AM
while we are on the subject heres a link i think you guys will like. it runs at 102 RPM
http://www.bath.ac.uk/~ccsshb/12cyl/
:eek:.....
:eek:.....
......108,920 hp at 102 rpm !!!!
now if we could just get the RPMs up to around 2000:evillol:.
http://www.bath.ac.uk/~ccsshb/12cyl/
:eek:.....
:eek:.....
......108,920 hp at 102 rpm !!!!
now if we could just get the RPMs up to around 2000:evillol:.
sierrap615
11-11-2004, 12:34 PM
i like the fact it takes 3 guys to install a bearing
curtis73
11-11-2004, 12:49 PM
1) What are ways that I can increase flow? A better exhaust would help out I know, but what about the valvetrain? What are the technical benefits of a SOHC (i.e. I4's) vs DOHC (i.e. V6's) vs the electronic Hydraulic systems of F1 cars vs any experimental things like the Coates CRVS (I know they have problems with sealing, but I'm talking about the theory behind it)? I know that the F1 systems are the best right now, but why (in technical terms)? And also why aren't there any companies making aftermarket headers using that technology?
You increase flow by changing intake, head, and valvetrain parameters. Exhaust is also important, but wait to design the exhaust until after the intake side is determined. Technical benefits of OHC designs include simplicity, less weight of moving parts, and longevity (in most cases). The SOHC is fine and allows for the simplicity part. The DOHC adds a little bit of design flexibility as far as where the valves go in the chamber.
2) I understand how Bore/stroke come into play, but are there any formulas for the trade off between them? Ex. if I wanted to keep the same displacement(power) but shorten the stroke, how would I figure out how much to increase the bore? Would it be a 1-to-1 ratio or something like that? Also I know the more you bore out an engine the weaker the walls of the chamber are, but are there any restrictions on shortening the stroke? And is there anyway to reinforce the combustion chambers walls to handle a higher bore?
You can just do the math. The engine's displacement is the area of one cylinder times the stroke times number of cylinders. The area of one cylinder is pi times radius squared, then multiply by the stroke. That gives you displaced volume of one cylinder. Then multiply it by number of cylinders. You will be able to just use the math to keep the same displacement.
Technically you can make the stroke as short as you want, but you reach a point of diminishing return. I'll talk more about this later, but if you shorten the stoke by half, you have cut your torque in half. You are using the same piston bore to exert the same force on a lever that is half as long. Cutting your torque in half cuts your HP in half. Now you have to spin the engine much faster to regain the HP you lost. In order to do that you have to massively increase breathing capability. I'll put this all together later...
3) I don't understand why I wouldn't be able to keep the low end power when I increase the RPM's of a low end engine like in my viper ex. It might be because I don't quite understand how an engines powerband is constructed. If someone could explain this in detail that would be AWESOME!!! Even just pointing me to a site with good charts would help me out a lot.
Here's why. I'm sure you've seen a dyno graph. The torque is a curve that usually goes up to its peak (around 4000 rpms in your example) then drops off again. If you just spun the engine faster, things like inertia, friction, and valvetrain events would start being a huge drag on it. The main reason the torque curve falls at higher RPMs is because it begins to require more torque to operate the engine than the engine can make. If you spun it faster, you would lose power. The way to change that is to do things like reduce weight of internal parts, and change how the engine breathes. Just spinning it faster is like asking you to run a marathon while breathing through a soda straw. You would be requiring more air than you could suck through the straw.
I'll give you the long answer now. :) Airflow in an engine is not a "more is better" proposition. There are two main things to look at in airflow qualities; flow, which is the amount of CFMs is possible to move, and velocity, basically the speed of the intake charge. Let's take the example of the soda straw to demonstrate flow. If you were watching movie on your couch, chances are it would be adequate. That is typical of a stock 5000-rpm engine. If you got up and went for a walk, it wouldn't be enough. So why not just always breathe through a 4" pipe, right? Always enough, but you only take what you need? This is where velocity plays a role. Cams have the valves open during intake an exhaust strokes, but they also overlap. Even a stock cam with 190 degrees duration is open 10 more degrees than one stroke which is 180 degrees. The exhast valve opens early to get rid of spent gasses before the piston starts back up. As the piston gets near the top, the intake valve opens early. Why? The outflow of exhaust is going really fast; fast enough to create a suction and start pulling in air from the intake valve. Intake air starts coming in before the piston starts sucking it in. The piston falls sucking in air/fuel. Again it creates a very fast moving column of air. So fast, that the inertia of the intake charge keeps filling the cylinder after the piston has reached the bottom. The intake valve closes after the cylinder has started back up for compression.
That was a little tangent to help you understand this: At very low RPMs you can see that this "ramming" effect would be small. The intake charge is moving slowly and the piston moves slower. At a certain RPM, this effect is maximized; for example, lets say 2500 RPMs in a mild stock engine. At 2500 RPMs, the stars align and the ramming effect of the intake charge is at its peak. Anywhere below 2500 RPMs, the intake charge doesn't have its peak velocity and doesn't fill the cylinders with as much charge. Above 2500 RPMs, the valve closes too quickly and doesn't get as much charge. This 2500 RPM peak value is where (or near) torque will peak. This is why all engine parts have to be matched together. Putting in a huge cam with lots of overlap will suck at low rpms. The ramming effect will be maximized at, say, 5000 rpms. At 5000 RPMs, the intake flow requirements are huge. This velocity also applies to the exhaust side. Above I mentioned that the speeding exhaust gasses create an inflow of intake. If you increase exhaust size too big, you've killed its velocity, and therefore its ability to suck in intake charge (which is called scavenging by the way)
If you offer up massive amounts of intake air potential to this engine with this cam, you will have a mismatch. Although flow is available, the velocity will have dropped. Without that velocity, the ramming effect that used to peak at 2500 will no longer be there and torque will suffer.
So, basically, the answer to your question boils down to the "straw" answer. Airflow characteristics on your viper engine example are fixed. The intake will keep up with flow to the peak of power, but then they can flow no more. Spinning it faster will be like running the marathon breathing through a straw. Conversely, if you add tons more air, you can spin faster and make more power (like running a marathon with a 4" pipe), but you've lost the ability to make lots of power at low RPMs.
I'm going to shut up now... I'm going to make some fake dyno graphs in a program I have to show you what happens to the power curves. I'll use a single engine, but change heads, cam, etc to show you how low end torque is lost with high-hp designs. Look for it later today or tomorrow.
You increase flow by changing intake, head, and valvetrain parameters. Exhaust is also important, but wait to design the exhaust until after the intake side is determined. Technical benefits of OHC designs include simplicity, less weight of moving parts, and longevity (in most cases). The SOHC is fine and allows for the simplicity part. The DOHC adds a little bit of design flexibility as far as where the valves go in the chamber.
2) I understand how Bore/stroke come into play, but are there any formulas for the trade off between them? Ex. if I wanted to keep the same displacement(power) but shorten the stroke, how would I figure out how much to increase the bore? Would it be a 1-to-1 ratio or something like that? Also I know the more you bore out an engine the weaker the walls of the chamber are, but are there any restrictions on shortening the stroke? And is there anyway to reinforce the combustion chambers walls to handle a higher bore?
You can just do the math. The engine's displacement is the area of one cylinder times the stroke times number of cylinders. The area of one cylinder is pi times radius squared, then multiply by the stroke. That gives you displaced volume of one cylinder. Then multiply it by number of cylinders. You will be able to just use the math to keep the same displacement.
Technically you can make the stroke as short as you want, but you reach a point of diminishing return. I'll talk more about this later, but if you shorten the stoke by half, you have cut your torque in half. You are using the same piston bore to exert the same force on a lever that is half as long. Cutting your torque in half cuts your HP in half. Now you have to spin the engine much faster to regain the HP you lost. In order to do that you have to massively increase breathing capability. I'll put this all together later...
3) I don't understand why I wouldn't be able to keep the low end power when I increase the RPM's of a low end engine like in my viper ex. It might be because I don't quite understand how an engines powerband is constructed. If someone could explain this in detail that would be AWESOME!!! Even just pointing me to a site with good charts would help me out a lot.
Here's why. I'm sure you've seen a dyno graph. The torque is a curve that usually goes up to its peak (around 4000 rpms in your example) then drops off again. If you just spun the engine faster, things like inertia, friction, and valvetrain events would start being a huge drag on it. The main reason the torque curve falls at higher RPMs is because it begins to require more torque to operate the engine than the engine can make. If you spun it faster, you would lose power. The way to change that is to do things like reduce weight of internal parts, and change how the engine breathes. Just spinning it faster is like asking you to run a marathon while breathing through a soda straw. You would be requiring more air than you could suck through the straw.
I'll give you the long answer now. :) Airflow in an engine is not a "more is better" proposition. There are two main things to look at in airflow qualities; flow, which is the amount of CFMs is possible to move, and velocity, basically the speed of the intake charge. Let's take the example of the soda straw to demonstrate flow. If you were watching movie on your couch, chances are it would be adequate. That is typical of a stock 5000-rpm engine. If you got up and went for a walk, it wouldn't be enough. So why not just always breathe through a 4" pipe, right? Always enough, but you only take what you need? This is where velocity plays a role. Cams have the valves open during intake an exhaust strokes, but they also overlap. Even a stock cam with 190 degrees duration is open 10 more degrees than one stroke which is 180 degrees. The exhast valve opens early to get rid of spent gasses before the piston starts back up. As the piston gets near the top, the intake valve opens early. Why? The outflow of exhaust is going really fast; fast enough to create a suction and start pulling in air from the intake valve. Intake air starts coming in before the piston starts sucking it in. The piston falls sucking in air/fuel. Again it creates a very fast moving column of air. So fast, that the inertia of the intake charge keeps filling the cylinder after the piston has reached the bottom. The intake valve closes after the cylinder has started back up for compression.
That was a little tangent to help you understand this: At very low RPMs you can see that this "ramming" effect would be small. The intake charge is moving slowly and the piston moves slower. At a certain RPM, this effect is maximized; for example, lets say 2500 RPMs in a mild stock engine. At 2500 RPMs, the stars align and the ramming effect of the intake charge is at its peak. Anywhere below 2500 RPMs, the intake charge doesn't have its peak velocity and doesn't fill the cylinders with as much charge. Above 2500 RPMs, the valve closes too quickly and doesn't get as much charge. This 2500 RPM peak value is where (or near) torque will peak. This is why all engine parts have to be matched together. Putting in a huge cam with lots of overlap will suck at low rpms. The ramming effect will be maximized at, say, 5000 rpms. At 5000 RPMs, the intake flow requirements are huge. This velocity also applies to the exhaust side. Above I mentioned that the speeding exhaust gasses create an inflow of intake. If you increase exhaust size too big, you've killed its velocity, and therefore its ability to suck in intake charge (which is called scavenging by the way)
If you offer up massive amounts of intake air potential to this engine with this cam, you will have a mismatch. Although flow is available, the velocity will have dropped. Without that velocity, the ramming effect that used to peak at 2500 will no longer be there and torque will suffer.
So, basically, the answer to your question boils down to the "straw" answer. Airflow characteristics on your viper engine example are fixed. The intake will keep up with flow to the peak of power, but then they can flow no more. Spinning it faster will be like running the marathon breathing through a straw. Conversely, if you add tons more air, you can spin faster and make more power (like running a marathon with a 4" pipe), but you've lost the ability to make lots of power at low RPMs.
I'm going to shut up now... I'm going to make some fake dyno graphs in a program I have to show you what happens to the power curves. I'll use a single engine, but change heads, cam, etc to show you how low end torque is lost with high-hp designs. Look for it later today or tomorrow.
Evil Result
11-11-2004, 05:07 PM
Could you combat port flow/velocity by increasing the number of cylinders while retaining the same total displacement.
If so this would mean the displacement of a single cylinder would decrease as would the port flow requirement at equal RPMs to a larger displacement cylinder.
If so this would mean the displacement of a single cylinder would decrease as would the port flow requirement at equal RPMs to a larger displacement cylinder.
Kurtdg19
11-11-2004, 06:39 PM
3) I don't understand why I wouldn't be able to keep the low end power when I increase the RPM's of a low end engine like in my viper ex. It might be because I don't quite understand how an engines powerband is constructed. If someone could explain this in detail that would be AWESOME!!! Even just pointing me to a site with good charts would help me out a lot.
One way that you can compromise an engine to get the max out of low rpms mid rpms and high rpms is to use different sets of cams and timming. I'm suprised nobody has mentioned variable valve timming yet (although I'm sure it would be on the way). Of coarse a Vipers ohv setup isn't practical to setup this way considering many things (one being the added valvetrain mass making it harder to rev vs. a OHC setup). There is a sticky at the top of the engineering page if you would like to learn more about variable valve timming.
One way that you can compromise an engine to get the max out of low rpms mid rpms and high rpms is to use different sets of cams and timming. I'm suprised nobody has mentioned variable valve timming yet (although I'm sure it would be on the way). Of coarse a Vipers ohv setup isn't practical to setup this way considering many things (one being the added valvetrain mass making it harder to rev vs. a OHC setup). There is a sticky at the top of the engineering page if you would like to learn more about variable valve timming.
curtis73
11-11-2004, 07:27 PM
Could you combat port flow/velocity by increasing the number of cylinders while retaining the same total displacement.
If so this would mean the displacement of a single cylinder would decrease as would the port flow requirement at equal RPMs to a larger displacement cylinder.
Yes, however two problems exist here. 1) when you divide the displacement over a greater number of cylinders, the surface area to stroke ratio changes, making the sum pressures of all cylinders combined less than what it was. 2) the smaller cylinders crutch airflow since when you drop diameter of the cylinder, the valve sizes have to be smaller. Although a greater percentage of the piston area can be composed of valve face, the effect is more than offset by the proximity of the cylinder walls shrouding the valves. Basically, your theory would be spot on, except for things like valve shrouding, harmonics, and other factors. The other thing is that (although you could engineer some of this out) the rotating mass in a 350 ci V10 would weigh more than a 350 ci V8.
You could keep the same bore and reduce stroke when you add cylinders, but there again, you are decreasing torque on the crankshaft. All in all its usually a wash.
Still working on dyno graphs.... More later.
If so this would mean the displacement of a single cylinder would decrease as would the port flow requirement at equal RPMs to a larger displacement cylinder.
Yes, however two problems exist here. 1) when you divide the displacement over a greater number of cylinders, the surface area to stroke ratio changes, making the sum pressures of all cylinders combined less than what it was. 2) the smaller cylinders crutch airflow since when you drop diameter of the cylinder, the valve sizes have to be smaller. Although a greater percentage of the piston area can be composed of valve face, the effect is more than offset by the proximity of the cylinder walls shrouding the valves. Basically, your theory would be spot on, except for things like valve shrouding, harmonics, and other factors. The other thing is that (although you could engineer some of this out) the rotating mass in a 350 ci V10 would weigh more than a 350 ci V8.
You could keep the same bore and reduce stroke when you add cylinders, but there again, you are decreasing torque on the crankshaft. All in all its usually a wash.
Still working on dyno graphs.... More later.
Reed
11-11-2004, 07:47 PM
comparing dohc to sohc i believe the sohc generaly have more torque but their top end power falls off cause they cant flow as much as a dohc. they get more torque cause they have less stuff to move, half as many cams and half as many valves.
the dohc motors have more stuff to move so get a little less torque but with twice as many valves it can flow more air and exhaust at higher rpms allowing for a more powerful top end.
the dohc motors have more stuff to move so get a little less torque but with twice as many valves it can flow more air and exhaust at higher rpms allowing for a more powerful top end.
curtis73
11-11-2004, 08:18 PM
Dyno charts. Two for now, more later if I get the time.
The first one pictured here is based on a typical street performance Buick 455; bore 4.313, stroke 3.900.
http://www.curtisandkim.com/dyno455street.jpg
This next one is based on an engine exactly half its size. I just took the dyno software and changed the 8 cylinders to 4 cylinders. It ends up being a Buick 228 4-cylinder.
http://www.curtisandkim.com/dyno455half.jpg
Take a look at both. They both make about 300 peak HP, but in order for the 4-cylinder to make that power, you have to more than double the airflow to each cylinder. Take a look at what it did to the torque, too. In order to get 300 hp from the 4-cylinder, I had to simulate 4-valve race heads, a single plane intake, and high flow headers. The important part I want you to get from the first graph is this. Take a look at power output at 8000 rpms. If you could get your engine to run that fast, it would be making zero output. It would be running, but at that point, the engine is making exactly the same power that it requires to overcome its own inertia and friction. Net power to the crankshaft would be zero. You had asked why you couldn't just run a viper V10 faster and have it make more power. There's your answer. After it passes the peak, it keeps making less power the faster it spins. In the graph above, the exponential increase in friction and air restriction meets up with the engine's abilities at 8000 RPMs.
There are obvioulsy pros and cons to each one. They both should produce similar acceleration, but the 4-cylinder needs a loose converter, short gearing, and in the end would most likely return less service life, poorer fuel mileage and less "streetability" It would idle very roughly, you couldn't operate any of your emissions equipment or your power brakes since it wouldn't create enough vacuum.
In addition, you would really notice the lack of torque on the street. With the 8-cylinder graph, you'd be able to drive it like a street car; without much thought. The 4-cylinder would require you to really rev it to get to the power you want.
Tomorrow's lesson -- :) Just kidding.-- Tomorrow I'll make up a couple more charts that show your V10 in street trim and race trim.
The first one pictured here is based on a typical street performance Buick 455; bore 4.313, stroke 3.900.
http://www.curtisandkim.com/dyno455street.jpg
This next one is based on an engine exactly half its size. I just took the dyno software and changed the 8 cylinders to 4 cylinders. It ends up being a Buick 228 4-cylinder.
http://www.curtisandkim.com/dyno455half.jpg
Take a look at both. They both make about 300 peak HP, but in order for the 4-cylinder to make that power, you have to more than double the airflow to each cylinder. Take a look at what it did to the torque, too. In order to get 300 hp from the 4-cylinder, I had to simulate 4-valve race heads, a single plane intake, and high flow headers. The important part I want you to get from the first graph is this. Take a look at power output at 8000 rpms. If you could get your engine to run that fast, it would be making zero output. It would be running, but at that point, the engine is making exactly the same power that it requires to overcome its own inertia and friction. Net power to the crankshaft would be zero. You had asked why you couldn't just run a viper V10 faster and have it make more power. There's your answer. After it passes the peak, it keeps making less power the faster it spins. In the graph above, the exponential increase in friction and air restriction meets up with the engine's abilities at 8000 RPMs.
There are obvioulsy pros and cons to each one. They both should produce similar acceleration, but the 4-cylinder needs a loose converter, short gearing, and in the end would most likely return less service life, poorer fuel mileage and less "streetability" It would idle very roughly, you couldn't operate any of your emissions equipment or your power brakes since it wouldn't create enough vacuum.
In addition, you would really notice the lack of torque on the street. With the 8-cylinder graph, you'd be able to drive it like a street car; without much thought. The 4-cylinder would require you to really rev it to get to the power you want.
Tomorrow's lesson -- :) Just kidding.-- Tomorrow I'll make up a couple more charts that show your V10 in street trim and race trim.
curtis73
11-12-2004, 12:12 AM
More dyno graphs
The first is a vague approximation of the Viper V10 in stock form:
http://www.curtisandkim.com/dynoviperstreet.jpg
This one is a hopped up version:
http://www.curtisandkim.com/dynoviperrace.jpg
Its important to note that I exxagerated the parts combo in the second graph to show a particularly poor torque curve. There are ways of adding power without killing your torque curve this severly, but for the sake of clear demonstration I really smacked the air flow to it without properly updating a few key parameters. In the first graph (the stock viper) notice that you get good torque through the entire band. Notice in the second graph that you have more power and a higher powerband, but torque at just-off-idle is below 200 ft-lbs compared to the nearly 500 you had before. In this case you gave up 300 ft-lbs of torque to get 80 hp. In reality you can choose parts that would keep almost the same torque at low rpms while adding power up high... In theory, adding flow without sacrificing velocity. That's the basic idea behind pocket porting heads. Alter the shape of the port to flow more without really adding much volume to slow it down. Fully porting heads is often a means to gain bulk flow with less regard to velocity.
That was an incredibly long answer to your question, nubtuner. You could spin a stock V10 faster in stock form, but as you can see from the first graph in this post, after 6000 RPMs it loses power fast. You'd do best in this car to shift at 5800 or 6000. Going beyond that, your acceleration would be hindered by the fact that you're using the engine in a band where it doesn't make much power. Contrast that with the theoretical second engine in this post, you would do best to shift at 7500. You would also need to reduce your rear gearing to help you get the RPMs up to where the engine makes power. You'll also have to go pick up the pieces of the shattered $9000 engine that just sent 10 pistons careening through the side of the block at 7200 rpms :D
The first is a vague approximation of the Viper V10 in stock form:
http://www.curtisandkim.com/dynoviperstreet.jpg
This one is a hopped up version:
http://www.curtisandkim.com/dynoviperrace.jpg
Its important to note that I exxagerated the parts combo in the second graph to show a particularly poor torque curve. There are ways of adding power without killing your torque curve this severly, but for the sake of clear demonstration I really smacked the air flow to it without properly updating a few key parameters. In the first graph (the stock viper) notice that you get good torque through the entire band. Notice in the second graph that you have more power and a higher powerband, but torque at just-off-idle is below 200 ft-lbs compared to the nearly 500 you had before. In this case you gave up 300 ft-lbs of torque to get 80 hp. In reality you can choose parts that would keep almost the same torque at low rpms while adding power up high... In theory, adding flow without sacrificing velocity. That's the basic idea behind pocket porting heads. Alter the shape of the port to flow more without really adding much volume to slow it down. Fully porting heads is often a means to gain bulk flow with less regard to velocity.
That was an incredibly long answer to your question, nubtuner. You could spin a stock V10 faster in stock form, but as you can see from the first graph in this post, after 6000 RPMs it loses power fast. You'd do best in this car to shift at 5800 or 6000. Going beyond that, your acceleration would be hindered by the fact that you're using the engine in a band where it doesn't make much power. Contrast that with the theoretical second engine in this post, you would do best to shift at 7500. You would also need to reduce your rear gearing to help you get the RPMs up to where the engine makes power. You'll also have to go pick up the pieces of the shattered $9000 engine that just sent 10 pistons careening through the side of the block at 7200 rpms :D
beef_bourito
11-12-2004, 11:49 AM
Wouldn't compression play a role in the high revs? I heard that F1 has super high compression. Most cars can't rev very high (+10,000) because the fuel can't burn fast enough right? At leased it's that way with deasels so shouldn't it apply to gasoline?
curtis73
11-12-2004, 11:59 AM
Wouldn't compression play a role in the high revs? I heard that F1 has super high compression. Most cars can't rev very high (+10,000) because the fuel can't burn fast enough right? At leased it's that way with deasels so shouldn't it apply to gasoline?
Yes and No. Diesels inject fuel directly into the cylinder and it burns slower, but is also injected through part of the power stroke. Gas gets it all at once, and once its burned its done. That is a BMEP discussion for another day.
Static compression ratio plays a big role as well in the airflow characteristics of the engine, but with the changes we're talking about, the big factor is dynamic compression; the actual compression based on static ratio and cam timing, VE, and other stuff. In the case of the second viper engine that I messed up, changing the static ratio between 8:1 and 11:1 wouldn't change power more than about 10hp since its mismatched.
You are correct, though. Provided all other factors are matched, a higher static compression ratio will provide better power at higher RPMs. This is mostly due to combustion efficiency flattening out the torque curve a touch. I won't get into the fuel burn rate discussion again; I've been flamed out of that too many times :biggrin:
Yes and No. Diesels inject fuel directly into the cylinder and it burns slower, but is also injected through part of the power stroke. Gas gets it all at once, and once its burned its done. That is a BMEP discussion for another day.
Static compression ratio plays a big role as well in the airflow characteristics of the engine, but with the changes we're talking about, the big factor is dynamic compression; the actual compression based on static ratio and cam timing, VE, and other stuff. In the case of the second viper engine that I messed up, changing the static ratio between 8:1 and 11:1 wouldn't change power more than about 10hp since its mismatched.
You are correct, though. Provided all other factors are matched, a higher static compression ratio will provide better power at higher RPMs. This is mostly due to combustion efficiency flattening out the torque curve a touch. I won't get into the fuel burn rate discussion again; I've been flamed out of that too many times :biggrin:
SaabJohan
11-13-2004, 01:43 PM
A DOHC four valve head has less mass to move than a two valve head, and especially when comparing to a push rod engine. Designed for a given power output the DOHC four valve head will also produce a higher torque throughout the whole rpm range while also reducing the stress in the valvetrain offer a better reliability and a lower cost in the long run.
The current F1 engines are designed for a life of 800 km, they are three litre V10 engines, each cylinder having a displacement of 300 cc from a bore of 96 to 99 mm. This means that the stroke is around 40 mm. The conrod has a length of about 2.5 times the stroke.
The engines use four gear driven camshaft, the valves are actuated through DLC coated finger followers. The engines has no conventional valve springs, they use pneumatic springs instead which allows the use of such high engine speeds. Compression ratio is somewhere around 13:1, to make the combustion chamber smaller than that would be difficult.
A F1 engine produces the same torque output like most three litre engines, but the high rpm make it possible to extract such high power levels, around 950 hp for the last of the 2004 engines. Idle is around 4000 rpm, max torque at around 15000 rpm and max power at around 18-19000 rpm (low 17k for the least powerful engines).
The engine manufacturers spend together around one billion dollars a year if I remember correctly, this is almost only for engine developement. The production cost is very low.
An F1 engine is designed for maximum power output, torque (curve) is only for driveability reasons. Engine weight is about 90-100 kg.
The engines use a small displacement because they are designed to be light and small to suit short and tricky tracks. This was decided after WW2 and has stayed the same, the regs just changes from time to time to reduce the power output for safety for example.
To be able to use engine speeds this high much developement work is spent to reduce friction, decrease combustion time, increase volumetric efficiency, optimise burn and so on.
The current F1 engines are designed for a life of 800 km, they are three litre V10 engines, each cylinder having a displacement of 300 cc from a bore of 96 to 99 mm. This means that the stroke is around 40 mm. The conrod has a length of about 2.5 times the stroke.
The engines use four gear driven camshaft, the valves are actuated through DLC coated finger followers. The engines has no conventional valve springs, they use pneumatic springs instead which allows the use of such high engine speeds. Compression ratio is somewhere around 13:1, to make the combustion chamber smaller than that would be difficult.
A F1 engine produces the same torque output like most three litre engines, but the high rpm make it possible to extract such high power levels, around 950 hp for the last of the 2004 engines. Idle is around 4000 rpm, max torque at around 15000 rpm and max power at around 18-19000 rpm (low 17k for the least powerful engines).
The engine manufacturers spend together around one billion dollars a year if I remember correctly, this is almost only for engine developement. The production cost is very low.
An F1 engine is designed for maximum power output, torque (curve) is only for driveability reasons. Engine weight is about 90-100 kg.
The engines use a small displacement because they are designed to be light and small to suit short and tricky tracks. This was decided after WW2 and has stayed the same, the regs just changes from time to time to reduce the power output for safety for example.
To be able to use engine speeds this high much developement work is spent to reduce friction, decrease combustion time, increase volumetric efficiency, optimise burn and so on.
bjdm151
11-15-2004, 02:01 PM
This is all very correct information except for one fact. The main limiting factor in incresing revs is piston acceleration. This is a factor that is determined by the rod stroke ratio. And is also one of the main factors in low speed port velocity. I don't have my notes on me, but i will try to bring formulas to post.
Pretty much an engine with a large bore stroke ratio (something typical of small block/big block v8's) have a long rod and stroke but a ratio of about 1:1. This produces a piston that accelerate and decelerates faster, which is a factor limiting speed because there is a limit to how fast you can accelerate the piston.
This also has an effect on the velocity the piston accelerates away from top dead center very quickly while something with a smaller ratio (F1 engines) move away from top dead center much slower.
Now don't curse me if i got my large/small ratios mixed up but i'll bring my notes in and pos a lot more good stuff.
And on a side note, i've done a lot of reaserch on fuel and flame speed and come up with a whole lot of nothing. One thing i do know is that F1 uses fuel that is very similar to pump gas (you can even run this stuff in your car). F1 fuel meets all European Union Standards for pump gasoline wich means that it is indeed very similar. At lower combustion temps (still trying to figure out actual temps,) the flame speed has very much to do with the volatility of fuel, but at higher temps it is more dependant upon the chemical nature of the fuel and much of the information on this reaction is still unknown.
hope this helps
Pretty much an engine with a large bore stroke ratio (something typical of small block/big block v8's) have a long rod and stroke but a ratio of about 1:1. This produces a piston that accelerate and decelerates faster, which is a factor limiting speed because there is a limit to how fast you can accelerate the piston.
This also has an effect on the velocity the piston accelerates away from top dead center very quickly while something with a smaller ratio (F1 engines) move away from top dead center much slower.
Now don't curse me if i got my large/small ratios mixed up but i'll bring my notes in and pos a lot more good stuff.
And on a side note, i've done a lot of reaserch on fuel and flame speed and come up with a whole lot of nothing. One thing i do know is that F1 uses fuel that is very similar to pump gas (you can even run this stuff in your car). F1 fuel meets all European Union Standards for pump gasoline wich means that it is indeed very similar. At lower combustion temps (still trying to figure out actual temps,) the flame speed has very much to do with the volatility of fuel, but at higher temps it is more dependant upon the chemical nature of the fuel and much of the information on this reaction is still unknown.
hope this helps
bjdm151
11-15-2004, 02:03 PM
I think the typical max acceleration for street vehicles is like 5700 fps
not quit sure so don't hate me if my numbers are wrong
not quit sure so don't hate me if my numbers are wrong
bjdm151
11-16-2004, 03:06 PM
Okay, back with my shit!
I was wrong, max safe rpm is dependent upon stroke.
The formula is (Stroke x RPM x 2) / 12 piston speed in feet per minute
Stroke is in inches
I was right on the part of rod stroke ratio determining some of the airflow characteristics of an engine.
I was wrong, max safe rpm is dependent upon stroke.
The formula is (Stroke x RPM x 2) / 12 piston speed in feet per minute
Stroke is in inches
I was right on the part of rod stroke ratio determining some of the airflow characteristics of an engine.
SaabJohan
11-17-2004, 06:07 AM
Typical piston accleration figures for a normal gasoline engine at max rpm is 23,000 m/s^2, mean piston velocity around 18 m/s, max velocity of 29 m/s at 75 and 285 deg ATDC.
A typical NASCAR Nextel Cup engine peaks at accelerations closer to 50,000 m/s^2, mean velocity of over 25 m/s and peak velocities above 40 m/s.
A typical F1 engine peaks at accelerations around 94,000 m/s^2, mean velocites 25 m/s, peak velocities of above 40 m/s at 80 and 280 deg ATDC.
These peak accelerations (which occur at TDC) are equal to:
Normal car engine: 2,300 G
NASCAR: 5,100 G
F1: 10,000 G
This means that during the acceleration a 230 gram F1 piston puts a force equal to 2,3 metric tons on the piston pin, which in turn put a force equal to 2,8 metric tons on the top of the con rod and so on.
The forces in the normal car engine isn't that much lower, perhaps half due to the higher weight of the reciprocating parts in those engines.
A typical NASCAR Nextel Cup engine peaks at accelerations closer to 50,000 m/s^2, mean velocity of over 25 m/s and peak velocities above 40 m/s.
A typical F1 engine peaks at accelerations around 94,000 m/s^2, mean velocites 25 m/s, peak velocities of above 40 m/s at 80 and 280 deg ATDC.
These peak accelerations (which occur at TDC) are equal to:
Normal car engine: 2,300 G
NASCAR: 5,100 G
F1: 10,000 G
This means that during the acceleration a 230 gram F1 piston puts a force equal to 2,3 metric tons on the piston pin, which in turn put a force equal to 2,8 metric tons on the top of the con rod and so on.
The forces in the normal car engine isn't that much lower, perhaps half due to the higher weight of the reciprocating parts in those engines.
bjdm151
11-17-2004, 11:13 AM
I can always count on this guy to come through with this shit.
Thanks again SaabJohan
Thanks again SaabJohan
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